Most natural gas consumed in the United States is not produced in the areas where it is most needed. To transport gas from increasingly remote production sites to consumers, pipeline companies operate and maintain hundreds of thousands of miles of natural gas transmission lines. This gas is then sold to local distribution companies, who deliver gas to consumers using a network of more than a million miles of local distribution lines. This vast underground transmission and distribution system is capable of moving many billions of cubic feet of gas each day. To provide force to move the gas, and to improve the economics of gas transportation, operators install large compressors at transport stations along the pipelines.
The single largest maintenance cost for a reciprocating compressor is compressor valves. Valve failures can primarily be attributed to high-cycle fatigue, sticking of the valve, accumulation of dirt and debris, improper lubrication and liquid slugs in the gas. Valves are designed for an optimal operation point; hence, valve operation is impaired when the operating conditions deviate significantly from the design point. In the traditional compressor valve design, an increase in valve life (reliability) directly relates to a decrease in valve efficiency. This relationship is due to an increase in valve lift (and flow-through area) being limited by the corresponding increase in the valve impact force. Above a certain impact velocity, valve plate failure is attributable to plastic deformation of the valve springs. These springs fail to provide adequate damping for the plate. The design of the valve springs is a major weakness in the valves currently in use. A lack of durability and low efficiency of the passive valve design demonstrates the need to control valve motion.